Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/tests.yml

@@ -16,7 +16,7 @@ jobs:
       fail-fast: false
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: php-actions/composer@v6
       - uses: php-actions/phpunit@v3
         with: